1. Field of the Invention
This invention relates to the protection of central office telephone switching apparatus from uneconomical tie up for long periods at times when a subscriber's line loop remains closed because the telephone handset is left off hook. Central office equipment is complex and expensive. It is for use when required but should not be tied up when there is no flow of communications. Experience has shown that a small percentage of subscribers will repeatedly, and for various reasons, intentionally leave the handset off the hook without attempting to place or complete a call within an allocated time interval. This condition creates a permanent signal that will tie up channels of the central office switching facilities and preclude their use by other subscribers. Common equipment in the central office is sufficient for normal traffic; however, a relatively small number of permanent signals is capable of blocking all traffic through the central exchange. It is desirable to identify the offending subscriber and the off hook condition and to release the subscriber's line circuit if his loop remains closed for prolonged intervals in which no attempt is made to complete a call.
The invention is applicable to manned telephone exchanges where a technician on duty is alerted by signals at the master test frame that an excessive number of subscribers have been routed to the permanent signal trunks. Tests are made by the technician to determine the cause of repeated trouble. If it is due to a receiving handset off hook the subscriber's line can be disconnected from the office equipment for the duration of each off hook condition if a permanent signal holding module, as embodied in this invention, is connected to his line. In #5 crossbar exchange offices the module is placed permanently on the lines of habitual offenders.
2. Description of the Prior Art
In the past one way to provide lockout has been to install extra automatic circuitry and relay devices in each line circuit of the plurality of suscribers. This is economically unattractive in view of the relatively small number of offenders and a very large number of total subscribers. Special effort has been made by other inventors to achieve balanced loads in each conductor of the line circuit to minimize noise. Another approach has been to connect the line circuit to a permanent signal trunk which is terminated so as to provide a high tone signal to the line and a busy signal to other subscribers.